EMBEDDED TOOL
Battery Life Estimator
Estimate runtime for a battery-powered project from capacity and average current draw.
Accounts for regulator losses and the fact that batteries rarely deliver their full rated capacity in practice — 85% is a common real-world estimate.
Estimated runtime
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In days
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Hover the chart to read remaining capacity at a given time. Assumes a constant average current draw.
About this tool
Estimate how long a battery-powered project will run, given the battery's capacity and the device's average current draw — the everyday calculation for sizing a battery pack for an ESP32, Arduino, or other embedded project. Includes an adjustable efficiency factor since real-world runtime is usually shorter than the naive capacity ÷ current division.
Frequently asked questions
- Why isn't runtime just capacity ÷ current?
- That naive figure assumes 100% of the rated capacity is usable at a constant rate, which real batteries rarely achieve — voltage sag, regulator conversion losses, temperature, and the discharge curve all reduce usable capacity, which is what the efficiency percentage approximates.
- How do I find my project's average current draw?
- If your device sleeps most of the time (like a sensor node), the average is a weighted blend of active and sleep current based on duty cycle — measure both with a multimeter or USB power meter and compute a time-weighted average rather than using the active current alone.
- Does this account for battery voltage?
- No — mAh capacity already factors out voltage, so this works the same way regardless of whether it's a single Li-ion cell, a AA pack, or a multi-cell battery, as long as the current draw was measured from that same battery.